Most breakfast cereals have what I would consider low fiber - like 3g. Milk with lactose also isn’t a great choice for a lot of people.
I’ve never heard of a low fiber diet for IBS. In fact the first dietary suggestion on the non-profit IFFGD’s website is to increase fiber intake:
https://aboutibs.org/treatment/ibs-diet/dietary-fiber/
I have heard of people having problems with fiber if they rapidly increase intake or if they don’t drink enough water. I target 1.5 to 2 gallons of water per day.
As you said, everyone is different but you’re just the first one I’ve heard aided by a low fiber diet.